In HLSL output, user-defined functions that have an array as their return value
get changed so that they have the array as an out parameter instead.

Still missing: support for calling a function that has array as a return value
without assigning the array. Also support for assignments inside complex
expressions.

TEST=dEQP-GLES3.functional.shaders.arrays.return.*
BUG=angleproject:941

Change-Id: I79f5170139116a3dcfb2be2df5f0f79a3d955ca8
Reviewed-on: https://chromium-review.googlesource.com/266003Reviewed-by: Olli Etuaho <oetuaho@nvidia.com>
Tested-by: Olli Etuaho <oetuaho@nvidia.com>